I have sailed several squaretop Formula 18s (Tiger, F18, Infusion). Those sails like a fairly stiff leech but it can easily be oversheeted so you have to pay attention. The top will stall first so you will have to sheet in to a stall then ease out to where the back telltails stream to see where the proper sheeting is for the wind conditions. I have found that even in very light winds the downhaul likes to be snugged on. This will open up the top as well. Not too much but it is something that you need to play with. The masts are getting bigger sections and that will throw another wrench into the mix...you will need to look closely at rotation.

Later,
Dan